Circulating epithelial tumor cells (CTCs) in peripheral blood are an ideal source for the detection of disseminated tumor cells of an easy sampling procedure. Their prognostic significance has been demonstrated in metastatic breast carcinoma and has the potential to influence the clinical management of patients with breast cancer. The aims of the present study are the evaluation of the prevalence and kinetics of CTS before and after anti-angiogenic treatment with bevacizumab (Avastin) in patients with metastatic breast cancer.

We analyzed 7.5 ml peripheral blood from 40 metastatic breast cancer patients treated with bevacizumab before (baseline) and after the first cycle of treatment. The presence of CTCs was assessed with the CellSearch System (Veridex, USA). Samples were subjected to immunomagnetic enrichment with an anti-EpCAM antibody and were fluorescence labeled. CTCs were defined as nucleated cells (DAPI+) expressing cytokeratin 8, 18 and 19 but CD45-negative phenotype. A sample was considered positive when one or more cells were detected.

Data are available for 40 patients. We found ≥ 1 CTCs before the first cycle of treatment with bevacizumab in 60% of the patients (n = 24). After the first treatment, reduction of one or more CTCs was found in 35% of the patients (n = 14). The median number of CTCs was 15 cells/7.5 ml blood in the first determination and 8 cells/7.5 ml in the second determination. In 30% of the patients (n = 12) we found an increase of baseline CTCs before and after treatment. In 26 patients we did not found any variation of baseline CTCs before and after treatment. In eight patients with CTCs positive at baseline (20%) the second determination after treatment was 0 cells/7.5 ml. Persistence of at least one CTC after the first cycle of treatment was found in 35% of the patients.

The results of this explorative study are preliminary and a large number of patients and follow-up are required. The study is ongoing to explore the prognostic significance of reduction or persistency of CTCs during treatment with anti-angiogenic agents (bevacizumab) and the relationship with response rate to treatment. Complete data will be presented.